如何使用Python抓取Web Canvas中RSI Estocástico折线图数据？

Hey Gustavo, solid question! Pulling data from a Web Canvas is tricky because it’s rendered as visual pixels instead of structured DOM elements, but let’s break down actionable ways to extract those blue/orange line values for the RSI Estocástico indicator:

1. First, check for hidden API or raw data sources (the easiest route) #

Most financial charting tools fetch raw data from a backend API before rendering it to Canvas. Here’s how to hunt for it:

• Open your browser’s Developer Tools (hit F12 or right-click > Inspect) and switch to the Network tab
• Clear existing requests, then follow your steps to add the "RSI Estocástico" indicator
• Filter requests by XHR or Fetch—look for calls with keywords like "rsi", "estocastico", or "indicator"
• Check the response body (usually JSON) for structured data—this will likely have the exact numerical values you need, no pixel hunting required
• If you find the right API endpoint, you can even call it directly to pull data without interacting with the Canvas at all

2. Parse pixel data from the Canvas (for cases where no API exists) #

If the site doesn’t expose raw data, you can use the Canvas API to analyze pixel colors and map them to values:

• First, locate the Canvas element in the Elements tab of Developer Tools (use document.querySelector('canvas') in the console to test)
• Grab its 2D context: const ctx = canvas.getContext('2d')
• Use ctx.getImageData(x, y, width, height) to get pixel data for the chart area
• Identify the exact RGB values of the blue/orange lines (use a color picker tool, or click a pixel in the Elements tab’s color inspector)
• Loop through the pixel data to find all points matching those colors, then map their positions to the chart’s axis scales (you’ll need to note the X-axis time range and Y-axis value range to calculate actual numbers)

3. Use browser scripts or extensions to automate the process #

• A Tampermonkey/Greasemonkey script can automate either the API check or Canvas parsing logic, saving you manual work
• Just be cautious with third-party extensions—stick to trusted tools, and always verify they comply with the site’s terms of service

Quick heads-up #

Make sure you’re allowed to scrape data from this site—double-check their robots.txt and usage policies to avoid any issues.

内容的提问来源于stack exchange，提问作者Gustavo Molina